Sung-Yung Lee

Near micron-sized cirrus cloud particles in high-resolution infrared spectra: An orographic case study

[1]xa0The high-resolution spectra of the Atmospheric Infrared Sounder (AIRS) provide a global view of small- particle-dominated cirrus clouds, and they exist over much larger spatial extents than seen in previous aircraft campaigns. As shown by simulations using a plane-parallel scattering radiative transfer (RT) model and realistic ice particle shapes, the shape of the radiance spectra in the atmospheric windows is uniquely influenced by small ice crystals. Minima in the brightness temperature (BT) spectra between 800 to 850 cm−1 are seen for ice particles smaller than 3 μm in the RT simulations and AIRS spectra. A case study of an orographic cirrus cloud observed on October 2, 2002, over the central Andes of South America is presented with spectral BT differences up to 63K between 998 and 811 cm−1.

The radiative consistency of Atmospheric Infrared Sounder and Moderate Resolution Imaging Spectroradiometer cloud retrievals

[1]xa0The consistency of cloud top temperature (TC) and effective cloud fraction (f) retrieved by the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU) observation suite and the Moderate Resolution Imaging Spectroradiometer (MODIS) on the EOS-Aqua platform are investigated. Collocated AIRS and MODIS TC and f are compared via an “effective scene brightness temperature” (Tb,e). Tb,e is calculated with partial field of view (FOV) contributions from TC and surface temperature (TS), weighted by f and 1−f, respectively. AIRS reports up to two cloud layers while MODIS reports up to one. However, MODIS reports TC, TS, and f at a higher spatial resolution than AIRS. As a result, pixel-scale comparisons of TC and f are difficult to interpret, demonstrating the need for alternatives such as Tb,e. AIRS-MODIS Tb,e differences (ΔTb,e) for identical observing scenes are useful as a diagnostic for cloud quantity comparisons. The smallest values of ΔTb,e are for high and opaque clouds, with increasing scatter in ΔTb,e for clouds of smaller opacity and lower altitude. A persistent positive bias in ΔTb,e is observed in warmer and low-latitude scenes, characterized by a mixture of MODIS CO2 slicing and 11-μm window retrievals. These scenes contain heterogeneous cloud cover, including mixtures of multilayered cloudiness and misplaced MODIS cloud top pressure. The spatial patterns of ΔTb,e are systematic and do not correlate well with collocated AIRS-MODIS radiance differences, which are more random in nature and smaller in magnitude than ΔTb,e. This suggests that the observed inconsistencies in AIRS and MODIS cloud fields are dominated by retrieval algorithm differences, instead of differences in the observed radiances. The results presented here have implications for the validation of cloudy satellite retrieval algorithms, and use of cloud products in quantitative analyses.

Nighttime cirrus detection using Atmospheric Infrared Sounder window channels and total column water vapor

[1]xa0A method of cirrus detection at nighttime is presented that utilizes 3.8 and 10.4 μm infrared (IR) window brightness temperature differences (dBT) and total column precipitable water (PW) measurements. This technique is applied to the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit A (AMSU-A) instrument suite on board EOS-Aqua, where dBT is determined from sets of carefully selected AIRS window channels, while PW is derived from the synergistic AIRS and AMSU-A water vapor retrievals. Simulated and observed dBT for a particular value of PW are not constant; several physical factors impact dBT, including the variability in temperature and relative humidity profiles, surface emissivity, instrument noise, and skin/near-surface air temperature differences. We simulate clear-sky dBT over a realistic range of PWs using 8350 radiosondes that have varying temperature and relative humidity profiles. Thresholds between cloudy and uncertain sky conditions are derived once the scatter in the clear-sky dBT is determined. Simulations of optically thin cirrus indicate that this technique is most sensitive to cirrus optical depth in the 10 μm window of 0.1–0.15 or greater over the tropical and subtropical oceans, where surface emissivity and skin/near-surface air temperature impacts on the IR radiances are minimal. The method at present is generally valid over oceanic regions only, specifically, the tropics and subtropics. The detection of thin cirrus, and other cloud types, is validated using observations at the Atmospheric Radiation Measurement (ARM) program site located at Manus Island in the tropical western Pacific for 89 coincident EOS-Aqua overpasses. Even though the emphasis of this work is on the detection of thin cirrus at nighttime, this technique is sensitive to a broad cloud morphology. The cloud detection technique agrees with ARM-detected clouds 82–84% of the time, which include thin cirrus, as well as other cloud types. Most of the disagreements are well explained by AIRS footprint-scale heterogeneity compared to ARM point measurements, cirrus overlying lower-layer water clouds, possible mixed phase microphysics in midlevel clouds, and significant IR channel noise for cold BT scenes over deep convective towers.

Standard and research products from the AIRS and AMSU on the EOS Aqua spacecraft

The Earth Science and Meteorological communities are taking great interest in a new instrument released by NASA. The Atmospheric Infrared Sounder (AIRS), launched on the EOS Aqua Spacecraft on May 4, 2002, is a high spectral resolution infrared imaging spectrometer with over 2300 distinct infrared wavelengths ranging from 3.7 μm to 15.4 μm. AIRS is unique in that it provides the highest infrared spectral resolution to date while also providing coverage of over 95% of the Earths surface every day at 15 km spatial resolution. The AIRS project is currently managed by NASAs Jet Propulsion Laboratory in Pasadena, California1. The AIRS is providing a wealth of scientific data to the Earth Science community including upper atmospheric water vapor and atmospheric composition on key greenhouse gases. It is also improving weather forecasting and the studies of processes affecting climate and weather.

AIRS/AMSU/HSB on EOS Aqua: first-year post-launch assessment

The Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit (AMSU), and Humidity Sounder from Brazil (HSB) are three instruments onboard the Earth Observing System (EOS) Aqua Spacecraft. Together, they form the Aqua Infrared and Microwave Sounding Suite (AIMSS). This paper discusses the science objectives and the status of the instruments and their data products one year after launch. All instruments went through a successful activation and calibration and have produced exceptional, calibrated, Level 1B data products. The Level 1B Product Generation Executables (PGEs) have been given to NOAA and the GSFC DAAC for production and distribution of data products. After nine months of operations, the HSB instrument experienced an electrical failure of the scanner. Despite the loss of HSB, early validation results have shown the AIRS and AMSU are producing very good temperature profiles.

Climate research with the atmospheric infared sounder

The Atmospheric Infrared Sounder (AIRS) sounding suite, launched in 2002, is the most advanced atmospheric sounding system to date, with measurement accuracies far surpassing those of current operational weather satellites. From its sun-synchronous polar orbit, the AIRS system provides more than 300,000 all-weather soundings covering more than 90% of the globe every 24 hours. Usage of AIRS data products, available to all through the archive system operated by NASA, is spreading throughout the atmospheric and climate research community. An ongoing validation effort has confirmed that the system is very accurate and stable and is close to meeting the goal of providing global temperature soundings with an accuracy of 1 K per 1-km layer and water vapor soundings with an accuracy of 20% throughout the troposphere, surpassing the accuracy of radiosondes. This unprecedented data set is currently used for operational weather prediction in a number of countries, yielding significant positive impact on forecast accuracy and range. It is also enabling more detailed investigations of current issues in atmospheric and climate research. In addition to the basic soundings related to the hydrologic cycle, AIRS also measures a number of trace gases, the latest such product being the global distribution of carbon dioxide. We discuss some examples of recent research with AIRS data.

Centroiding accuracy of infrared Earth images mitigating impact of blurring and Earth non-uniformity

Infrared (IR) Earth thermal image tracking has potential to enable optical communications throughout the solar system and is a promising alternative to traditionally proposed laser beacon tracking. Image blurring due to finite receiver aperture size introduces distortions to IR Earth image in the presence of Earths non-uniform emissivity and reduces the centroiding accuracy in identifying the center of the Earth. The impact is largest in the 0.5 to 2 AU range. We demonstrate that a deconvolution algorithm can mitigate the effect of blurring associated with IR Earth non-uniformity and improve centroiding edge detection accuracy.

Eight Years of AIRS

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched in May of 2002. The AIRS Sounding Suit, AIRS along with AMSU-A and HSB, were designed to measure the atmospheric temperature and water vapor profiles, the surface and the cloud parameters for climate research and for improvement in weather forecast. Over the last 8+ years AIRS has been operating extremely stable, far surpassing original design life of 4 - 5 years. Many exciting research papers on climate have been published with AIRS data. The AIRS data are assimilated by most NWP centers and have shown considerable improvement in forecast skill. We will describe the current status of the instruments as well as the new activity on the data processing software.

The atmospheric infrared sounder: an overview

The Atmospheric Infrared Sounder (AIRS) was launched in May 2002. Along with two companion microwave sensors, it forms the AIRS Sounding Suite. This system is the most advanced atmospheric sounding system to date, with measurement accuracies far surpassing those available on current weather satellites. The data products are calibrated radiances from all three sensors and a number of derived geophysical parameters, including vertical temperature and humidity profiles, surface temperature, cloud fraction, cloud top pressure, and ozone burden. These products are generated under cloudy as well as clear conditions. An ongoing calibration/validation effort has confirmed that the system is very accurate and stable, and most of the geophysical parameters have been validated. AIRS is in some cases more accurate than any other source and can therefore be difficult to validate, but this offers interesting new research opportunities. The applications for the AIRS products range from numerical weather prediction to atmospheric research - where the AIRS water vapor products near the surface and in the mid to upper troposphere will make it possible to characterize and model phenomena that are key for short-term atmospheric processes, such as weather patterns, to long-term processes, such as interannual cycles (e.g., El Niño) and climate change.